Demai, Chapter Four, Mishnah Seven
The previous mishnah dealt with the fear that merchants might collude, each paying compliments to the others produce. Our mishnah deals with another instance in which we might fear that two merchants are colluding.
If donkey-drivers entered a city and one of them declared: My produce is new but my friends produce is old, or, My produce has not been tithed but my friends produce has been tithed, they may not be trusted.
Rabbi Judah says: they may be trusted.
Two donkey drivers enter the city each carrying loads of produce. Each one testifies that his produce is new or untithed (bad) but that his friends produce is old or tithed (both good). In other words, each compliments his friends produce and denigrates his own. In this case, according to the first opinion, we should suspect that they are colluding and we may not trust either of them.
Rabbi Judah says that there is reason to be lenient also in this case and to trust them. Donkey drivers who bring supplies to the city are necessary for the good of the city. Were the people of the city not to trust them, they might not come back. Therefore, they too can be trusted.